Comparative studies of selection in
M2 and M3 generations have revealed that in many
cases the two populations may not differ in response to selection (4,5).
On the other hand, some experiments have demonstrated that selection in M3
is more effective than in M2 (1,2). This was, most probably,
because the material already selected in M2 was confirmed with
higher probability in subsequent generations (3). Even if the material
selected in M3 or later generations has a higher probability of
becoming fixed as promising strains, there is no evidence to suggest that
the frequency of promising mutations perse is higher in M3
than in M2. It-can be argued that the variability manifested in
M3 could not have arisen afresh without causing any impact on the
M2 population. Therefore in the present study selection was
initiated in the M2 generation on the basis of higher CV
(variability) and desired shift in mean than the highest values in these
parameters in the control (untreated population) for five polygenic traits
(days to flowering, pods/plant, seeds/pod, 100-seed weight and
yield/plant). The criterion for confirmation of the promising families in
M3 was the shift in mean values in the desired direction. The
selection efficiency in M2 generation, calculated on the basis
of this criterion, is presented in Tables 1 and 2.

As can be seen from Table 2,
76.2-79.8% of M2 selections were confirmed as promising in the
M3 generation. This suggests that selection in M2 was very
effective and dependable. Some characters showed an increase in variance
with the advance in generation to M3, which is confirmed by the
fact that a further 22.2-24.8% of promising progenies were identified in M3.
Nevertheless, early generation selection is of great help in reducing the
volume of work, in saving time, and in isolation of confirmed mutations.
As can be seen from Table 2, the contribution of the M2 and M3
generations to total selections arising from the different treatments was
75.2-77.8% and 22.2-24.8%, respectively. Thus, although new mutated
progenies (about one-fourth of total) were added in the M3
generation (progenies which were either not identified in M2 or
were new additions as a result
of release of additional variability), the volume of material has to be
increased very substantially in order to recover this smaller additional variability of a
promising nature.

The overall analysis of the results
obtained reveals that there is tremendous possibility to improve polygenic
characters through induced mutagenesis by employing an efficient selection
technique. It is evident that rigorous selection can help identify
promising variants from the mutagenized populations in the first
segregating (M2) generation. These variants can simultaneously
be confirmed and their potential tested in the M3
generation.